Implantable coronary sinus lead with mapping capabilities

ABSTRACT

A cardiac lead is disclosed that includes a first lead body having opposed proximal and distal end portions and an interior lumen extending therethrough. The first lead body includes a sensor for measuring blood flow parameters to facilitate placement of the distal end portion thereof adjacent the coronary sinus. The first lead body has a distal electrode operatively associated with the distal end portion thereof and a proximal electrode operatively associated with the proximal end thereof. The second lead body has opposed proximal and distal end portions. A distal electrode is operatively associated with the distal end portion thereof and a proximal electrode operatively associated with the proximal end thereof. The second elongated lead body is dimensioned and configured for accommodation within the interior lumen of the first lead body.

CROSS-REFERENCE TO RELATED APPLICATIONS

The subject application is a continuation-in-part of U.S. applicationSer. No. 09/912,796 filed Jul. 25, 2001 and a continuation-in-part ofU.S. application Ser. No. 10/000,647 filed Nov. 11, 2001.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The subject invention is directed to an intravenous lead, and moreparticularly, to an implantable cardiac lead and having mappingcapabilities to facilitate safe placement of the lead within thecoronary sinus.

2. Background of the Related Art

Electrical therapeutic and diagnostic devices for the heart, such aspacemakers and defibrillators, commonly employ leads for connecting anelectrical pulse generator to excitable cardiac tissue, usually withinthe right ventricle and/or right atrium. Pacing and defibrillation leadscommonly include one or more distal electrodes and often have outwardlyprojecting tines near the distal tip or an active fixation screw to holdthe electrode in contact with endocardial tissue in the right ventricleor atrium.

It has been found that cardiac stimulation can have a beneficial effectin treating congestive heart failure. However, pacing therapy fortreating congestive heart failure often requires left ventricularstimulation, either alone or in conjunction with right ventricularstimulation and defibrillation. Left ventricular pacing presentlyrequires placement of an epicardial lead by way of a thoracotomy, whichis a high risk procedure performed under general anesthesia. To obviatethe need for a thoracotomy, left ventricular access leads have beendeveloped which are introduced through the coronary sinus and thenadvanced through the coronary veins so that the distal electrode of leadcan be positioned on the surface of the left ventricle near the apex ofthe heart.

The coronary veins of the heart are of a relatively small diameter. Thelead extended therethrough must therefore, be of a relatively smalldiameter, as compared to leads used for right ventricular stimulation.Cardiac and respiratory motion as well as blood flow can cause a lead tobecome dislodged. Accordingly, the lead must include structure to anchorthe electrode at a desired location.

It would be beneficial to provide a left ventricular pacing leadconfigured for advancement through the coronary sinus and into thecoronary vein, which has structure for anchoring the distal end of thelead at a desired site of stimulation, and which could be used incertain instances for defibrillation.

SUMMARY OF THE INVENTION

The subject invention is directed to a new and useful implantablecardiac lead adapted and configured for advancement through the coronarysinus and into the coronary vein that includes cooperating first (outer)and second (inner) elongated lead bodies. The first lead body hasopposed proximal and distal end portions, an interior lumen extendingtherethrough, at least one distal electrode operatively associated withthe distal end portion thereof and a proximal electrode operativelyassociated with the proximal end thereof. Preferably, the first leadbody includes sensor means that are operatively associated with thedistal end portion thereof for measuring blood flow parameters tofacilitate placement of the distal end portion of the first lead bodyadjacent the coronary sinus, and seal means for sealing the interiorlumen of the first lead body during insertion of the first lead bodythrough the coronary venous system.

The second (inner) lead body has opposed proximal and distal endportions, at least one distal electrode operatively associated with thedistal end portion thereof, a proximal electrode operatively associatedwith the proximal end thereof, and it is dimensioned and configured foraccommodation within the interior lumen of the first (outer) lead body.Preferably, the proximal end portion of the first lead body and theproximal end portion of the second lead body include means forconnecting the first lead body to the second lead body.

In accordance with the subject invention, the second lead body has alength that is greater than the length of the first lead body.Preferably, the length of the first lead body is about between 50 and 80cm, and the length of the second lead body is about between 60 and 100cm. preferably, the outer diameter of the first lead body is aboutbetween 6 and 9 F, and the outer diameter of the second lead body isabout between 3 and 5 F.

A conductor extends through the first lead body to connect the distalelectrode and the proximal electrode, and a conductor extends throughthe second lead body to connect the distal electrode and the proximalelectrode. Additionally, the second lead body has an interior lumenextending therethrough to accommodate a stylet. In one embodiment of theinvention, the distal electrode of the first lead body is a ringelectrode spaced from the distal end of the lead body for pacing and/orsensing. Alternatively, the distal electrode of the first lead body is acoil electrode used for defibrillation, or as a ground electrode. In oneembodiment of the invention, the distal electrode of the second leadbody is a ring electrode that is spaced from the distal end of thesecond lead body for pacing and/or sensing. Alternatively, the distalelectrode of the second lead body is configured as tip electrode forpacing and/or sensing. The proximal electrode of the second lead body ispreferably defined as a pin connector.

The second or inner lead body preferably has fixation means operativelyassociated with the distal end portion thereof for anchoring the leadwithin the coronary venous system. In addition, the first or outer leadbody may have fixation means operatively associated with the distal endportion thereof. In either case, the fixation means may be defined by atleast one radially expandable tine, by an expandable stent configuredfor movement between a retracted position and an expanded position, orby a plurality of radially expandable arms configured for movementbetween a retracted position and an extended position. Furthermore, thefixation means may have a coating containing a medicament such as asteroid.

The subject invention is also directed to a new and useful method ofimplanting a cardiac lead comprising the steps of passing an elongatedouter lead body having an interior lumen through the venous system to aselected coronary vein, and extending an elongated inner lead body intothe interior lumen of the outer lead body so that a distal end portionof the inner lead body extends from a distal end portion of the outerlead body.

The method further includes that steps of securing the inner and outerlead bodies to one another, and anchoring at least one of the distal endportion of the inner lead body and the distal end portion of the outerlead body within the selected coronary vein. The step of anchoring atleast one of the distal end portion of the inner lead body and thedistal end portion of the outer lead body within the selected coronaryvein includes deploying an expandable stent operatively associated withat least one of the distal end portion of the inner lead body and thedistal end portion of the outer lead body, or deploying expandable armsoperatively associated with at least one of the distal end portion ofthe inner lead body and the distal end portion of the outer lead body.

These and other aspects of the subject invention and the method of usingthe same will become more readily apparent to those having ordinaryskill in the art from the following detailed description of theinvention taken in conjunction with the drawings described hereinbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

So that those having ordinary skill in the art to which the subjectinvention pertains will more readily understand how to make and use thecardiac lead of the subject invention, preferred embodiments thereofwill be described in detail hereinbelow with reference to the drawings,wherein:

FIG. 1 is a perspective view of the two-part coronary sinus leadconstructed in accordance with a preferred embodiment of the subjectinvention, the distal end of which is in electrical contact with theleft ventricle of the heart through the great cardiac vein;

FIG. 2 is a perspective view of the two-part coronary sinus lead of thesubject invention which includes an outer lead body having an anodicring electrode associated with the distal end portion thereof, and aninner lead body configured for accommodation within the interior lumenof the outer lead body and having a cathodic tip electrode associatedwith the distal end thereof;

FIG. 3a is a side-elevational view, in partial cross-section, of thedistal end portion of the outer lead body, with the tapered distal tipthereof in an initially sealed condition to facilitate ease ofintra-vascular introduction;

FIG. 3b is a side elevational view, in partial cross-section, of theproximal end portion of the outer lead body;

FIG. 3c is a side elevational view, in partial cross-section, of thedistal end portion of the inner lead body;

FIG. 3d is a side elevational view, in partial cross-section, of theproximal end portion of the inner lead body;

FIG. 4 is a side elevational view of the coronary sinus lead of thesubject invention, with the proximal coupling of the inner lead bodypartially sectioned to illustrate the threaded engagement of theproximal end portions of the inner and outer lead bodies;

FIG. 5 is a side elevational view of another embodiment of the coronarysinus lead of the subject invention configured for left ventricularpacing and sensing;

FIG. 6 is a side elevational view of another embodiment of the coronarysinus lead of the subject invention configured for left ventricularpacing and sensing, and for right ventricular defibrillation;

FIG. 7 is a side elevational view of another embodiment of the coronarysinus lead of the subject invention configured for left ventricularpacing and sensing, and for right atrial pacing and sensing.

FIG. 8 illustrates the placement of the outer lead body of the coronarysinus lead of FIG. 5, through the superior vena cava to a positionadjacent the auriculo-ventricular opening to the coronary sinus;

FIG. 9 illustrates the placement of the inner lead body through theinterior lumen of the outer lead body and into the great cardiac vein ofthe heart through the coronary sinus;

FIGS. 10a and 10 b illustrate the retracted and extended positions,respectively, of an anchoring device associated with the distal endportion of the inner lead body;

FIGS. 11a and 11 b illustrate the contracted and expanded positions,respectively, of an expandable stent operatively associated with thedistal end portion of the inner lead body;

FIGS. 12 and 13 illustrate additional embodiments of an expandablefixation device operatively associated with the distal end portion ofthe inner lead body;

FIG. 14 illustrates the deployment of the coronary sinus lead of FIG. 6which is configured for left ventricular pacing and sensing, inconjunction with a second lead configured for right ventricular pacingand sensing, as well as defibrillation;

FIG. 15 illustrates the deployment of the coronary sinus lead of FIG. 7which is configured for left ventricular and right atrial pacing andsensing, in conjunction with a second lead configured for rightventricular pacing and sensing, as well as defibrillation; and

FIG. 16 illustrates another embodiment of the coronary sinus lead of thesubject invention wherein the a sensor is operatively associated withthe distal end portion of the outer lead body for measuring blood flowparameters to facilitate placement of the distal end portion of theouter lead body adjacent the opening to the coronary sinus.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to the drawings wherein like reference numerals identifysimilar structural features of the intravenous leads disclosed herein,there is illustrated in FIG. 1 a coronary sinus lead constructed inaccordance with a preferred embodiment of the subject invention anddesignated generally by reference numeral 10. Coronary sinus lead 10 isadapted and configured for intravenous introduction to the great cardiacvein or branch vein through the coronary sinus so that an electrodeassociated with a distal end portion of the lead is in electricalcontact with the left ventricle of the heart. The proximal end of thelead is then operatively connected to an implanted therapeuticelectrical device such as a pacemaker. Once in contact, the distalelectrode of lead 10 may be employed for left ventricular pacing and/orsensing.

Referring to FIGS. 2 and 3a-3 b, coronary sinus lead 10 includes anouter lead body 12 and an inner lead body 14 configured for receptionand accommodation within an interior lumen of the outer lead body. Moreparticularly, the outer lead body 12 has opposed distal and proximal endportions 16 and 18, and an interior lumen 20 extending therethrough. Thedistal end portion 16 of lead body 12 is tapered to ease theintravascular placement thereof. A distal electrode 22 is operativelyassociated with the distal end portion 16 and a proximal electrode 24 isoperatively associated with the proximal end portion 18. The distalelectrode 22 is in the form of a ring electrode, as is the proximalelectrode 24. However, other types of electrode configurations can beemployed for purposes other than sensing and/or pacing as will bedescribed in more detail hereinbelow. The proximal and distal electrodes22, 24 of the outer lead body 12 are electrically connected to oneanother by a conductor such as a monofilliar or multifilliar coil 23,and they serve as the anode for coronary sinus lead 10. The proximal endportion 18 of the outer lead body 12 has a connective device operativelyassociated therewith for cooperating with a complimentary structure onthe proximal end portion of the inner lead body 14. More particularly,the proximal end portion 18 of the outer lead body 12 has a helicalthread 26 formed on an exterior surface thereof, spaced from or formedintegral with the proximal electrode 24.

Referring to FIGS. 2 and 3c-3 d, the inner lead body 14 has opposeddistal and proximal end portions 36 and 38 and an interior lumen 40 foraccommodating a stylet (not shown) to guide placement of the lead in thegreat cardiac vein. The inner lead body 14 has a distal electrode 42operatively associated with the distal end portion 36 and a proximalelectrode 44 operatively associated with the proximal end portion 38.The distal electrode 42 is in the form of a ring electrode, as is theproximal electrode 44. However, other types of electrode configurationscan be employed for purposes other than sensing and/or pacing as will bedescribed in more detail hereinbelow. Proximal electrode 44, forexample, can be configured as a connector pin with an axial bore foraccommodating passage of a stylet. The proximal and distal electrodes42, 44 of the inner lead body are electrically connected to one anotherby a conductor such as a monofiliar or multifiliar coil 43, and theyserve as the cathode for coronary sinus lead 10. The proximal endportion 38 of the outer lead body 14 has a connective device in the formof an end cap 46 with an interior helical thread 48 for cooperating withthe helical thread 26 associated with the proximal end portion 18 ofouter lead body 12.

It is envisioned that the conductor coils 23, 43 used to connect therespective distal and proximal electrodes of the inner and outer leadbodies could be formed from an insulated wire. The wire could be a lowresistance wire such as, for example, MP35N or DFT wire, and theinsulative coating could be PTFE, polyamide, silicone or a similarmaterial.

Those skilled in the art will readily appreciate that alternativemechanisms may be employed to interconnect the proximal ends of theouter and inner lead bodies 12, 14 without departing from the spirit orscope of the subject disclosure. Moreover, the illustrated threadedconnective mechanism, which is referred to in the art as an IS-1 typeconnector, is merely an example of a connector that may be employed withthe inner and outer lead bodies 12, 14.

As illustrated in FIG. 4, the inner lead body is dimensioned andconfigured for accommodation within the interior lumen 20 of the outerlead body in such a manner so that the distal end portion 36 of theinner lead body 14 extends from the distal end portion 16 of the outerlead body 12. In particular, the length of the outer lead body 12 isabout between 50 and 80 cm, and the length of the inner lead body 14 isabout between 60 and 100 cm. Thus, the distal end portion 36 of theinner lead body 14 extends from the interior lumen 20 of the outer leadbody about between 10 and 20 cm. The outer diameter of the outer leadbody 12 is about between 6 and 9 F, and the outer diameter of the innerlead body 14 is about between 3 and 5 F. Those skilled in the art willreadily appreciate that the dimensions disclosed herein could varywithout departing from the scope of the invention.

Referring now to FIG. 5, there is illustrated another coronary sinuslead constructed in accordance with a preferred embodiment of thesubject invention and designated generally by reference numeral 100.Coronary sinus lead 100 is similar to coronary sinus lead 10 in that itis configured for left ventricular pacing and sensing. Lead 100 differshowever in that the outer lead body 112 includes a distal groundelectrode 122 and the inner lead body 114 includes a distal tipelectrode 142.

FIG. 6 illustrates another coronary sinus lead constructed in accordancewith a preferred embodiment of the subject invention and designatedgenerally by reference numeral 200. Coronary sinus lead 200 isconfigured for left ventricular pacing and sensing, and for rightventricular defibrillation. More particularly, the inner lead body 214includes a distal tip electrode 242 (in conjunction with proximal ringelectrode 244) for pacing and/or sensing, and the outer lead body 212includes an elongated distal ground electrode or coil 222 forfacilitating right ventricular defibrillation in conjunction with asecond cardiac lead which will be discussed in greater detainhereinbelow with reference to FIG. 14.

FIG. 7 illustrates yet another coronary sinus lead constructed inaccordance with a preferred embodiment of the subject invention anddesignated generally by reference numeral 300. Coronary sinus lead 300is configured for left ventricular pacing and sensing, and for rightatrial pacing and sensing. More particularly, the inner lead body 314has a distal tip electrode 342 for pacing and/or sensing, and the outerlead body 312 includes distal ring electrode 322 a for right atrialpacing/sensing and an elongated distal ground electrode 322 b forfacilitating right ventricular defibrillation in conjunction with asecond cardiac lead which will be discussed in greater detainhereinbelow with reference to FIG. 15. In this embodiment, proximal ringelectrode 344 is provided on inner lead body 314 and proximal ground anright atrial electrodes 324 a and 324 b are associated with outer leadbody 312.

The tip, ring and ground electrodes employed on the inner and outer leadbodies are preferably formed from a platinum/iridium alloy, as is thecoiled shock electrode. The inner and outer lead bodies are preferablyformed from silicon, polyurethane, PTFE or a similar bio-compatibleinsulative plastic or elastomer.

In accordance with an embodiment of the subject invention, the coronarysinus lead includes a fixation member operatively associated with thedistal end portion of the inner lead body. The fixation member isadapted and configured to anchor the lead within the coronary sinusagainst the flow of blood and the cardiac pressure of the beating heart.Preferably, the fixation member has a polymeric coating containing amedicament that is released into the vascular tissue over time. Thepolymeric coating is preferably absorbable, and the medicament ispreferably a steroid or a similar therapeutic drug for treating thecardiac tissue surrounding the distal end of the lead. Non-polymericcoating s may also be used to carry a medicament for absorption. It isalso envisioned that the fixation member can be electrically active soas to function as a distal electrode for pacing and/or sensing.

Referring to FIGS. 10a-10 b, one embodiment of the fixation member isdesignated generally by reference numeral 50. Fixation member 50includes a pair of radially expandable arms 52 a and 52 b which extendfrom an annular base structure 54. The arms 52 a, 52 b are formed from abio-compatible material, such as stainless steel, or a shape memorymetal such as a nickel-titanium alloy. Fixation member 50 is operativelyassociated with the distal end portion 36 of the inner lead body and ismounted for movement between a retracted position (FIG. 10a) whereinarms 52 a, 52 b are disposed within the interior lumen 40 of inner leadbody 14 and an extended position (FIG. 10b) wherein arms 52 a, 52 bextend radially outwardly to anchor lead body 14 against longitudinaldisplacement. In use, fixation member 50 may be deployed from theretracted position to the extended position by extending an elongatedstylet or similar structure through the interior lumen 40 of inner leadbody 14. It is envisioned that the distal end of lumen 40 would beadapted to limit the movement of the base structure 54 beyond a certainpoint to maintain it within the interior lumen.

Referring to FIGS. 11a-11 b, another embodiment of the fixation memberis designated generally by reference numeral 60. Fixation member 60 isdefined by a radially expandable vascular stent formed from abio-compatible polymeric material or metal that may be braided or cutfrom a tubular structure. It is envisioned that the stent would movefrom a contracted position to a radially expanded position when exposedto body temperature, or in response to retracting a sheath (not shown)initially disposed about the stent during its placement within a bloodvessel.

FIGS. 12 and 13 illustrate two other embodiments of a fixation memberincluding a radially expandable cylindrical coil 70 and a radiallyexpandable wire cage 80. These fixation devices may be constructed anddeployed in a manner similar to fixation member 60. It is envisionedthat the distal end portion 16 of the outer lead body 12 may alsoinclude a fixation member in the form of any one of the previouslydescribed fixation structures or at least one flexible tine as is knownin the art. The fixation member associated with the distal end portionof the outer lead body 12 could be electrically active and/or providedwith a coating containing a medicament.

Referring now to FIGS. 1, 5, 8 and 9, by way of example, coronary sinuslead 10 is deployed in the following manner for facilitating leftventricular pacing and/or sensing. Initially, as illustrated in FIG. 8,with the assistance of a guiding stylet or catheter (not shown), theouter lead body 12 is extended into the right atrium of the heartthrough the superior vena cava to a position adjacent to theauriculo-ventricular opening to the coronary sinus. At such time, thedistal tip of the outer lead body 12 is in a closed or sealed condition.In this position, the distal ground electrode 22 (anode) of the outerlead body 12 is disposed within the right atrium. Thereafter, asillustrated in FIG. 9, the inner lead body 14 is introduced into thecoronary sinus by way of the interior lumen 20 of the outer lead body12. In essence, the outer lead body 12 serves as a guide catheter tofacilitate the placement of the inner lead body 14 into the coronarysinus and subsequent introduction into the great cardiac vein or branchvein.

The inner lead body 14 is advanced into the great cardiac vein or branchvein to a location where the distal tip electrode 42 (cathode) ispositioned so as to be in contact with the wall of the left ventricle,as best seen in FIG. 1. Then, as shown for example in FIG. 4, theproximal end portions 18, 38 of the outer and inner lead bodies 12, 14are threadably connected to one another so as to form an integralstructure. At such a time, either one of the fixation devices 50, 60, 70or 80 may be deployed from the distal end portion 36 of the inner leadbody 14 to prevent longitudinal displacement of lead 10. Furthermore, asimilar fixation structure operatively associated with the distal endportion 16 of the outer lead body 12 may be deployed within the rightatrium to maintain the position of lead 10. Once lead 10 has been fullydeployed and the two lead bodies 12, 14 have been threadably connectedto one another, the lead 10 is operatively connected to a cardiacpacemaker so that it may be employed for left ventricular pacing and/orsensing.

Referring now to FIG. 14 in conjunction with FIG. 6, coronary sinus lead200 is employed to facilitate left ventricular pacing and/or sensing inconjunction with a second lead 250 configured for right ventricularpacing and sensing, as well as defibrillation. More particularly, lead200 is deployed in the manner described above with respect to lead 10.Lead 250 is extended into the right ventricle by way of the superiorvena cava and is secured therein by a conventional fixation structure,such as, for example, a helical fixation screw. As illustrated, lead 250includes a distal tip electrode 252 for pacing and/or sensing and adistal shock electrode 254 for right ventricular defibrillation. Theground for defibrillation is supplied by the elongated proximalelectrode 224 of the outer lead body 212.

Referring to FIG. 15 in conjunction with FIG. 7, coronary sinus lead 300is employed to facilitate left ventricular and right atrial pacing andsensing, in conjunction with a second lead configured for rightventricular pacing and sensing, as well as defibrillation. Moreparticularly, lead 300, which is deployed in the manner described abovewith respect to lead 10 to facilitate left ventricular pacing and/orsensing, right atrial pacing and/or sensing, and right ventriculardefibrillation. As in the previous deployment shown in FIG. 14, lead 250is extended into the right ventricle by way of the superior vena cavaand includes a distal tip electrode 252 for pacing and/or sensing and adistal shock electrode 254 for right ventricular defibrillation inconjunction with the proximal ground electrode 322 b of outer lead body312.

Referring now to FIG. 16, there is illustrated another embodiment of thecoronary sinus lead of the subject invention designated generally byreference numeral 400. In this embodiment, the distal end portion of theouter lead body includes a sensor 445 for monitoring blood flowparameters. The blood flow sensor 445 can take the form of an ultrasonicpulse Doppler sensor, transit-time sensor or a similar sensor. Suchsensors are known in the art as disclosed for example in U.S. Pat. No.5,409,009 to Olson, the disclosure of which is herein incorporated byreference in its entirety.

Although the coronary sinus lead and placement method of the subjectinvention has been described with respect to preferred embodiments,those skilled in the art will readily appreciate that changes andmodifications may be made thereto without departing from the spirit andscope of the present invention as defined by the appended claims.

What is claimed is:
 1. A cardiac lead comprising: a) a first elongatedlead body having opposed proximal and distal end portions and having aninterior lumen extending therethrough, the first lead body includingmeans operatively associated with the distal end portion thereof formeasuring blood flow parameters to facilitate placement of the distalend portion of the first lead body adjacent the coronary sinus, andhaving at least one distal electrode operatively associated with thedistal end portion thereof and a proximal electrode operativelyassociated with the proximal end portion thereof; and b) a secondelongated lead body having opposed proximal and distal end portions, thesecond lead body having at least one distal electrode operativelyassociated with the distal end portion thereof and a proximal electrodeoperatively associated with the proximal end portion thereof, whereinthe second elongated lead body is dimensioned and configured foraccommodation within the interior lumen of the first lead body.
 2. Acardiac lead as recited in claim 1, wherein the means operativelyassociated with the distal end portion of the first lead body formeasuring blood flow parameters is defined by a blood flow sensor.
 3. Acardiac lead as recited in claim 1, wherein the second lead body has alength that is greater than the length of the first lead body.
 4. Acardiac lead as recited in claim 1, wherein a conductor extends throughthe first lead body to connect the distal electrode and the proximalelectrode.
 5. A cardiac lead as recited in claim 1, wherein a conductorextends through the second lead body to connect the distal electrode andthe proximal electrode.
 6. A cardiac lead as recited in claim 1, whereinthe second lead body has an interior lumen extending therethrough.
 7. Acardiac lead as recited in claim 1, wherein the distal electrode of thefirst lead body is a ring electrode.
 8. A cardiac lead as recited inclaim 1, wherein the distal electrode of the first lead body is a coilelectrode.
 9. A cardiac lead as recited in claim 1, wherein the distalelectrode of the first lead body is a ground electrode.
 10. A cardiaclead as recited in claim 1, wherein the distal electrode of the secondlead body is a ring electrode.
 11. A cardiac lead as recited in claim 1,wherein the distal electrode of the second lead body is a tip electrode.12. A cardiac lead as recited in claim 1, wherein the distal electrodeof the first lead body is anodic, and the distal electrode of the secondlead body is cathodic.
 13. A cardiac lead as recited in claim 1, whereinthe proximal electrode of the second lead body is a pin connector.
 14. Acardiac lead as recited in claim 1, wherein the first lead body includesseal means for sealing the interior lumen of the first lead body duringinsertion of the first lead body through the coronary venous system. 15.A cardiac lead as recited in claim 1, wherein the proximal end portionof the first lead body and the proximal end portion of the second leadbody include means for connecting the first lead body to the second leadbody.
 16. A cardiac lead as recited in claim 15, wherein the means forconnecting the first lead body to the second lead body includes athreaded connector.
 17. A cardiac lead comprising: a) a first elongatedlead body having opposed proximal and distal end portions and having aninterior lumen extending therethrough, the first lead body having asensor operatively associated with the distal end portion thereof formeasuring blood flow parameters to facilitate placement of the distalend portion of the first lead body adjacent the coronary sinus, andhaving at least one distal electrode operatively associated with thedistal end portion thereof and a proximal electrode operativelyassociated with the proximal end portion thereof; and b) a secondelongated lead body having opposed proximal and distal end portions, thesecond lead body having at least one distal electrode operativelyassociated with the distal end portion thereof and a proximal electrodeoperatively associated with the proximal end portion thereof, whereinthe second elongated lead body is dimensioned and configured foraccommodation within the interior lumen of the first lead body.